The present invention relates to a method for preparing high purity sulfinic acids.
Many methods have been employed to produce sulfinic acids. One of the most widely used methods is the reduction of sulfonyl halogenides with, for example, zinc, iron, aluminum or magnesium. The product yields from this reduction method, however, are low and the products themselves require additional processing to produce the desired sulfinic acids because the reduction partially goes beyond the sulfinic acids to disulfides or mercaptans.
Oxidation methods where sulfur containing organic compounds are oxidized also have been used to produce sulfinic acids, but these oxidation methods are among the less popular methods that have been used to produce sulfinic acids. For example, in one known oxidation method sodium thioethylate (C.sub.2 H.sub.5 --SNa) has been oxidized with dry oxygen. In another prior art oxidation method, sulfhydryl groups containing substituted aromatic or heterocyclic compounds have been treated with chlorine, an alkali potassium permanganate solution or with a 30% solution of hydrogen peroxide. In still another oxidation method, aryl sulfacids have been brought in contact with air, an alkali medium or potassium hexacyanoferrate (III). All prior art oxidation methods, however, have the drawback that the oxidation reactions cannot be controlled and thus a partial further oxidation of the sulfinic acids to sulfonic acids occurs and cannot be avoided. Accordingly, in the prior art oxidation methods, it is necessary to use further time consuming and relatively complicated processing techniques such as an additional processing method for treating the mixture to convert the sulfonic acid and form sulfinic acid or a method for separating the sulfinic acids from the sulfonic acids.